The present invention generally relates to the fabrication of optical components in limited rotation motor systems, and relates in particular, to the fabrication of such components having high stiffness and low inertia.
Scanning mirror systems generally include a mirror surface that is either mounted on a substrate or is formed as part of a substrate, wherein the substrate is coupled to a shaft of a motor system. Such motors may either run continuously (e.g., for use with a polygonal mirror) or such motors may be limited rotation motors providing movement within a limited angular range. These applications require that the mirror be as stiff as possible consistent with a minimum of inertia as they are accelerated back and forth over the limited angular range.
In typical limited rotation scanning systems (also called galvanometer systems) a mirror is mounted to the output shaft of a limited rotation motor and the limited rotation motor is controlled by a control loop that seeks to cause the rotor of the motor, and therefore the mirror, to follow a position and velocity command waveform with arbitrarily high fidelity.
There are limits, however, on the fidelity with which the system may follow the command. For example, the acceleration of the mirror within the system is limited by the rate of rise of current in the motor windings. The positional precision is limited by the signal to noise ratio of the feedback method. The bandwidth of the system (which is its ability to move from position A to position B at a desired high velocity and to then settle at position B precisely in the shortest possible time), is limited primarily by vibrations in the moving parts. The bandwidth of the system will nominally be ½ the first torsional resonance in the moving structure.
It is customary, therefore, to make the moving parts as stiff as possible within the constraints of the allowable system inertia. Since the torque required of the motor to reach a specified acceleration is directly proportional to the inertia and is proportional to the current (whose rate of rise is limited as noted above), it is often the case that when the system parameters are optimized for a particular inertia, some component, typically the mirror, even when made of a very high stiffness-to-inertia material, is not as stiff as is required to reach system bandwidth goals. In this case, extra material is added to the mirror to increase its stiffness, but, at the cost of additional inertia, requiring a larger, more expensive motor as well as a control loop that is capable of driving the additional inertia.
There is a need therefore, for a limited rotation motor system that provides improved bandwidth without requiring a larger, more expensive motor and accompanying control system.